How to call to a class object at the class itself?

Question

I'm new at Python and I'm trying to do something and hope you can help me:
If I'm defining a class at Python like: class foo:, and inside the class I want to do something with "foo" object, i.e. - I want that one of the objects of the class will be something like a=foo().

So, it should look like:

 class foo:
     def __init__(self):
         self.t=7

     a=foo() #it's outside init....

It is possible? There is a way to do it?
(I'm trying to do this and it's always give me errors...)
(I tried to do import to the file but it doesn't help at all...)

Thank you!

You need to create a function in class, and then you may do it within the function — Moinuddin Quadri, Dec 04 '16 at 18:54
Are you trying to write a Singleton pattern? http://stackoverflow.com/questions/31875/is-there-a-simple-elegant-way-to-define-singletons-in-python — ziggy jones, Dec 04 '16 at 19:12

score 1 · Answer 1 · answered Dec 04 '16 at 18:58

1

Do it after the class definition:

class Foo:
    pass

Foo.a = Foo()

answered Dec 04 '16 at 18:58

kindall

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Yes, it's an attribute of the class, just as if you had defined it in the class definition. – kindall Dec 04 '16 at 19:05
`NameError: name 'foo' is not defined` – Yoar Dec 04 '16 at 19:36
Ah yeah, you musta caught my answer in the brief window while I had that typo in it. As to your other comment, yeah, it's part of the class; see for yourself! – kindall Dec 04 '16 at 20:30

score 0 · Answer 2 · edited Dec 04 '16 at 21:36

0

No. at the stage you define a = foo, foo is not defined. However, you can create a variable for foo instance inside foo like:

class Foo:
  def __init__(self):
    pass

  a = None

Foo.a = Foo()

edited according to the comments.

edited Dec 04 '16 at 21:36

interjay

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answered Dec 04 '16 at 19:10

Musen

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That won't work. The instance `a` will shadow the class `a`. – Dan D. Dec 04 '16 at 19:11
where is the class `a` ? – Musen Dec 04 '16 at 19:12
@juanpa.arrivillaga Not actually needed for this purpose, but without it one cannot call Foo.a before doing `Foo.a = Foo()`. – Musen Dec 04 '16 at 19:26
Of course you can. `class Foo: pass; Foo.a = Foo()` is perfectly valid Python. – juanpa.arrivillaga Dec 04 '16 at 19:28
@juanpa.arrivillaga Yes, but I mean you cannot do things like `if isinstance(Foo.a, Foo)`. – Musen Dec 04 '16 at 19:35
Well, you could use error handling, but why is that relevant? – juanpa.arrivillaga Dec 04 '16 at 19:36
@juanpa.arrivillaga Not perfectly relevant. You can say it is an unnecessary personal practice. – Musen Dec 04 '16 at 19:41
I think you meant to write `a = None` inside the class definition. Doing it on an instance variable (`self.a`) wouldn't let you access `Foo.a` before assigning a value. – interjay Dec 04 '16 at 19:56
@interjay You are correct. It is an error. Thank you! – Musen Dec 04 '16 at 20:18
It still wouldn't work (it would gave an error because `self` doesn't exist). I edited it to something that does work. – interjay Dec 04 '16 at 21:37
@interjay Yes, it was a typo. Thank you for the editing! – Musen Dec 04 '16 at 21:38

How to call to a class object at the class itself?

2 Answers2